The present invention is directed to a method of modifying poly(ethylene oxide). More particularly the present invention is directed to modified poly(ethylene oxide) that crosslinks upon exposure to moisture and is also melt processable. The present invention also relates to articles made from modified poly(ethylene oxide) that are capable of absorbing relatively large amounts of fluid.
Disposable personal care products, such as pantiliners, diapers, tampons etc., are a great convenience. Such products provide the benefit of one time, sanitary use and are convenient because they are quick and easy to use. However, disposal of such products is a concern due to limited landfill space. Incineration of such products is not desirable because of increasing concerns about air quality and the costs and difficulties associated with separating such products from other disposed, non-incineratable articles. Consequently, there is a need for biodegradable personal care products.
Poly(ethylene oxide) (xe2x80x9cPEOxe2x80x9d) is one of a very few polymers that is both water-soluble and thermally processable. PEO has also been shown to be biodegradable under a variety of conditions. Initial work was done with PEO N-80 (molecular weight xcx9c200.000) which is commercially available from Union Carbide. This grade of PEO is suitable for extrusion processing into film. However, the resultant films have relatively low tensile strength. Ions ductility, and brittleness. Typical values are 12 MPa break stress and elongation at break of 220%. In an unmodified form, high molecular weight PEO is not thermally processable. Melt fracture and excessive vaporization are observed as PEO is extruded. The resulting resins cannot be cast into thin films and do not have properties that are useful for personal care applications.
A key requirement to achieve a substantially biodegradable personal care product, such as a diaper is to identify and utilize a biodegradable absorbent material that provides the expected levels of leakage protection. There is a wide variety of biodegradable polymers with the potential to become a functional absorbent, but in the current state of development, none provide the leakage protection of sodium polyacrylates. However, sodium polyacrylates are not appreciably degraded in mixed microbial systems unless they are so low in molecular weight (500-700 g/mol) that they are not functional as absorbents.
Consequently, there is a need for biodegradable, absorbent personal care products that are made from materials that can be relatively easily processed, such as by thermal processing, so that it can be easily fabricated into a wide range of structures, such as films, foams, and fibrous webs. Currently available water-soluble resins are not practical for melt processing thin films or fibers for personal care applications. What is needed in the art, therefore, is a water soluble resin that overcomes the difficulties associated with melt processing while also possessing good saline absorption characteristics and functional forms made therefrom are still absorbent, flexible and biodegradable. Examples of water-soluble resins include poly(alkylene oxides) such as PEO; poly(ethylene glycols), block copolymers of ethylene oxide and propylene oxide, poly(vinyl alcohol) or poly(alkyl vinyl ethers).
The present invention is directed to methods for improving saline absorption characteristics of functional forms made from the silane craft modified PEO of the present invention while maintaining the melt processability of silane graft modified PEO as quell as the softness and flexibility of personal care products made therefrom. More particularly, the present invention relates to methods of modifying PEO to improve its saline absorption characteristics while retaining its melt processability by grafting organic monomers containing trialkoxy silane functional groups, such as methacryloxypropyl trimethoxy silane, or a moiety that reacts with water to form a silanol group, onto the PEO. The grafting is accomplished by combining PEO; silane-containing monomer(s), an initiator and applying heat. In a preferred embodiment, the method of modification is a reactive-extrusion process. PEOs modified in accordance with this invention have improved water absorption characteristics and melt processabilities and can be thermally processed into films, fibers, foams and other articles which have improved properties over films, fibers, foams and articles similarly processed from unmodified PEO compositions.
To overcome the disadvantages of the prior art, this invention teaches a method of grafting trialkoxy silane functional group-containing organic monomers or monomers containing a moiety that reacts with water to form a silanol group, onto PEO in the melt. Modification of PEO produces a polymer that does not crosslink during melt processing, but rather can be processed into functional forms, such as fibers, films, foams and the like. Yet, when these functional forms made from the modified polymer of the present invention are exposed or subjected to relatively high moisture conditions, they crosslink with each other and form a gel that is capable of absorbing relatively large amounts of saline. Additionally, modified PEO resins in accordance with the present invention can be solidified into pellets for later thermal processing into useful shapes, such as films, fibers, foams and other useful forms which are in turn useful as components in personal care products. The resulting personal care products are soft and flexible and biodegradable.
As used herein, the term xe2x80x9cgraft copolymerxe2x80x9d means a copolymer produced by the combination of two or more chains of constitutionally or configurationally different features, one of which serves as a backbone main chain, and at least one of which is bonded at sonic point(s) along the backbone and constitutes a side chain. As used herein, the term xe2x80x9cgraftingxe2x80x9d means the forming of a polymer by the bonding of side chains or species at some point(s) along the backbone of a parent polymer. (See Sperling, L. H., Introduction to Physical Polymer Science 1986 pp. 44-47 which is incorporated by reference herein in its entirety.)
Modification of PEO resins with starting molecular weights of between about 3,350 g/mol and 8,000,000 g/mol are useful in the present invention. Modification of PEO resins with starting molecular weights of between about 300,000 g/mol to about 8,000,000 g/mol allows the modified PEO resins to be drawn into films with thicknesses of less than about 0.5 mil. Modification of PEO resins with starting molecular weights of between about 400,000 g/mol to about 8,000,000 g/mol is preferred for filmmaking. Films drawn from the modified PEO compositions have better softness, flexibility, and greater clarity than films drawn from unmodified low molecular weight PEO. Thermal processing of films from high molecular weight PEO modified in accordance with this invention also results in films with improved mechanical properties over films similarly processed from unmodified low molecular weight PEO films.
Modification of PEO resins with starting molecular weights of between about 50,000 g/mol to about 400,000 g/mol allows the modified PEO resins to be extruded into fibers using conventional melt spinning processes. Modification of PEO resins with starting molecular weights of between about 50,000 g/mol to about 200,000 g/mol is preferred for fiber making. The modification of PEO in accordance with this invention improves the melt properties of the PEO allowing the modified PEO to be melted and attenuated into fibers. Thus, the modified PEO can be processed into water-absorbent fibers using both meltblown and spunbond processes which are useful for liners, cloth-like outer covers, etc. in flushable personal products. The modified PEO can be processed into water-absorbent staple fibers for use in bonded carded webs or in airlaid structures.
These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.